EMBODIED CARBON IN A BUILDING’S LIFE CYCLE

Embodied carbon is determined by conducting a life-cycle assessment (LCA) of a product, assembly, or building over declared life- cycle stages. An LCA study returns results for a number of environmental metrics, including the potential to impact climate or “global warming potential” (GWP). Embodied carbon is the GWP result. Embodied carbon is measured for each stage of the product’s life cycle, allowing comparisons across any combination of stages.

As buildings become more energy efficient, the upfront embodied carbon from materials begins to account for a higher proportion of a building’s carbon footprint²³. Very soon, embodied carbon is likely to become the dominant source of building emissions.

Embodied carbon varies dramatically between concrete, steel and wood, making product decisions key in achieving lower carbon buildings. Manufacturing wood products requires less total energy, and in particular less fossil energy, than manufacturing alternative structural materials including metals, concrete, or bricks²⁴.

STORED CARBON IN WOOD PRODUCTS

Wood products are approximately 50% carbon by dry weight²⁵. The use of wood products in buildings provides an additional environmental benefit by storing carbon removed from the atmosphere. This ability to store carbon sequestered during tree growth in the forest makes wood an ideal product for buildings, which are designed for long service lives. Essentially, a wood building is a large carbon sink²⁶.

Timber as a tactic for curbing climate change is backed by a growing body of research and advancements in calculating the carbon footprint of building materials²⁷. In a recent paper published in the journal Nature Sustainability, experts at the Potsdam Institute for Climate Impact Research²⁸ in Germany delved into four possible scenarios of timber use in buildings over the next 30 years. In the first case, “business as usual,” 0.5% of buildings are made with wood while the vast majority remain constructed of concrete and steel. There’s a 10% timber building scenario; a 50% timber building scenario; and a fourth in which the vast majority—90% of new construction—is made with wood. Their findings suggest that the lowest scenario could result in 10 million tons of carbon stored per year and in the highest, nearly 700 million tons²⁹.

“Buildings, which are designed to stay for decades,” researchers write in the paper, “are an overlooked opportunity for a long-term storage of carbon, because most widely used construction materials such as steel and concrete hardly store any carbon."³⁰

THE ROLE OF WOOD CONSTRUCTION NOW AND IN THE FUTURE

There is an urgent need to decarbonize the built environment, combat climate change and find advanced ways to reduce and store carbon emissions. The exigency to cut carbon is demonstrated by the environmental priorities set by such organizations as C40 Cities³¹, Architecture 2030³², Urban Land Institute³³, and the World Green Building Council³⁴ advocating for significant changes in how we plan, build, manage, and power cities and towns—including a reduction in embodied carbon over a building’s life cycle. Wood has an increasing role to play as design professionals look to tackle the climate crisis and reduce the environmental footprint of buildings, now and in the future.

Buildings and infrastructure built from bio-based materials such as timber that store carbon during their service lives can serve as constructed carbon sinks. They could increase the existing carbon pool of urban areas (1–12 GtC) by 25 to 170%³⁵. Backed up by testing and research, code changes in jurisdictions across the country are making it possible to increase the height and density of wood construction. With a comprehensive understanding of these code changes, design teams can bring innovation and ingenuity to the buildings they design.

ADDITIONAL RESOURCES

To help building designers compare options, WoodWorks has compiled a web-based inventory of completed mass timber fire tests. The Inventory of Fire Resistance Tested Mass Timber Assemblies & Penetrations is updated as new tests become available and can be found at www.woodworks.org.

For additional information on both the calculation-based method and the ASTM E119 testing method of demonstrating FRR of mass timber elements, see the WoodWorks publication Fire Design of Mass Timber Members.

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